1. Field of the Invention
The present invention relates to a magnetic head actuator having a finely movable tracking device and, more particularly, to a power feeding structure for wiring to a piezoelectric element of the tracking device.
2. Description of the Related Art
A magnetic head actuator widely used in an HDD is provided with a magnetic head opposing a rotating hard disk. The magnetic head is positioned at the free end of a swing arm, which swings reciprocally around the rotation axis of the base of the swing arm. In accordance with tracking signals from the hard disk, the actuator allows the swing arm to swing around the rotation axis. In order to meet the demand for a narrower track width or a smaller track pitch, a finely movable tracking device is constructed, such that a piezoelectric element, which expands and contracts when a voltage is applied, is mounted in the swing arm. Thus, the free end of the swing arm makes a fine arcuate movement around the rotation axis of the arm in accordance with expansion and contraction of the piezoelectric element.
In a conventional magnetic head actuator provided with the finely movable tracking device, a ground electrode of the piezoelectric element is electrically connected to the swing arm, and power is supplied to a voltage-impressing electrode via a feeding line of a flexible printed circuit (FPC) board that extends along the swing arm. The feeding line of the FPC board and the voltage-impressing electrode of the piezoelectric element are bonded by conventional gold (Au) wire bonding.
The Au wire bonding, however, is not only expensive due to the many man-hours required but also the Au wire bond is easily broken by an external force applied to the thin Au wire, which has a diameter on the order of a few micrometers. Also, a component, such as a magnetic head actuator that is incorporated into an HDD in an additional step after assembly the wiring is easily broken, thereby leading to continuity defects and low yield.
The present invention provides a magnetic head actuator with a finely movable tracking device that which facilitates wiring to a piezoelectric element, while reducing problems such as wire breakage and continuity defects in the wiring.
The present invention facilitates connecting a voltage-impressing electrode of a piezoelectric element and a feeding line of an FPC board without using Au wire bonding. To this end, the feeding line of the FPC board is arranged to extend onto the voltage-impressing electrode, where an exposed portion is formed by removing a resin base of the FPC board that extends onto the electrode. Also, an electrical and mechanical connection to the electrode at the exposed portion is made by ultrasonic bonding, Au ball bonding or stud bumping.
A magnetic head actuator having a finely movable tracking device according to the present invention comprises a swing arm having a magnetic head at the free end of the swing arm, the swing arm being reciprocally movable around a coarse rotation axis of the base of the swing arm; a piezoelectric element, mounted in the swing arm, for allowing a fine arcuate movement of the free end around the coarse rotation axis when a voltage is applied; and an FPC board having a resin base and a feeding line embedded in the resin base for feeding power to a voltage-impressing electrode. The feeding line of the FPC board is arranged to extend onto the voltage-impressing electrode of the piezoelectric element. The feeding line has an exposed portion formed by removing the resin base from a portion of the feeding line extending onto the electrode and a direct electrical connection is made to the electrode at the exposed portion.
In another aspect of the present invention, in the magnetic head actuator, the feeding line of the FPC board is arranged to extend onto the voltage-impressing electrode of the piezoelectric element. The feeding line lies in the FPC board other than the portion to be bonded to the piezoelectric element. A direct electrical connection is made to the electrode at the exposed portion of the feeding line.
Specifically, as used herein, electrical conduction means any mechanical and electrical bonding, and may include ultrasonic bonding, Au ball bonding, and the like.
Preferably, the feeding line arranged to extend onto the voltage-impressing electrode of the piezoelectric element is partially exposed at the upper and lower portions of the feeding line. After a through-hole is formed at the exposed portion, a gold ball is inserted into the through-hole and the feeding line is electrically bonded to the electrode by gold ball bonding. Alternatively, after forming a stud bump made of conductive material on the piezoelectric element, the feeding line is electrically connected to the electrode by inserting the stud bump into the through-hole of the feeding line.
Although a swing arm can provide a single piezoelectric element in a preferred embodiment of the invention, the swing arm is provided with a pair of piezoelectric elements having polarities opposite to each other so that the magnetic head makes a larger movement.
Although an FPC board having a feeding line leading to the piezoelectric element can be prepared separately, in a preferred embodiment the FPC board includes a trace line leading to the magnetic head and extending in the FPC board.
Thus, the present invention provides a magnetic head actuator, provided with a finely movable tracking device using a piezoelectric element that facilitates wiring to the piezoelectric element while reducing problems such as wire breakage and continuity defects.